What color is a tennis ball?

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Noam Hassenfeld (0:56)

A while back, I was at physical therapy. I was doing some stretching. I was talking to people. We were talking about tennis. And at what point someone said something about yellow tennis balls. And I was like, no, they're green. And then someone else was like, no, they're yellow. And then someone across the room was like, no, they're obviously green.

The next day, I come into physical therapy, and there's one of those questions above the water fountain, like where it's normally, what's your favorite sandwich or what's your favorite holiday or something.

This time, it was, what color are tennis balls? And it was pretty much even. It caused like this physical therapy uproar. And when I asked people how they voted, they told me they just couldn't even believe there was a debate. So I called up Bevil Conway. He's a neuroscientist who heads up a lab at the National Eye Institute. He's working on a book called Color Coded. It's going to be out next year. And he's also a working artist. That's actually how he got into studying color in the first place.

And Bevil told me there's a pretty good reason for why so many people disagree about tennis balls. He said, it's simple.

Bevil Conway (2:09)

There's no such thing as a color.

Noam Hassenfeld (2:11)

Today, Unexplainable, what? Bevil Conway, thanks for coming on the show.

Bevil Conway (2:32)

Oh my God. It's so much fun to be here.

Noam Hassenfeld (2:35)

So, you are an artist, you are also a neuroscientist, you study color, you're also working on a book about color.

Are there still color mysteries? Are there things science doesn't know about color?

Bevil Conway (2:52)

There are lots of mysteries about color. I think, for a long time, people thought that color was a filter. Everything that's really important is in black and white, and then there's a color filter you put on top of it.

Noam Hassenfeld (3:09)

Just like a decoration.

Bevil Conway (3:11)

A decoration, yeah. A bunch of years ago, my lab were blown away to discover that there's as much brain involved in processing color as there is in face recognition.

Noam Hassenfeld (3:23)

The same amount of brain processing power?

Bevil Conway (3:25)

There's tons and tons of tissue in pretty fancy bits of brain that are doing pretty high-level things, like parts of brain we think of as being involved in social cognition and in high-level reasoning and visual memory. Color must be more than just this little add-on. It's doing something much deeper.

So we're trying to understand what those bits of brain are doing.

Noam Hassenfeld (3:49)

So before we get into all of those mysteries, I wonder if we can just kind of get on some solid ground. Sure.

What is color and how does it work? How does our brains and eyes perceive it?

Bevil Conway (4:04)

Sure. So color, I think the classic definition would be color is the visual feature that you get from the spectral composition or the wavelength properties of the light entering your eye. People typically see the long wavelength end as red light and then going through short wavelengths, following Roy G. Biv, red, orange, yellow, green, blue, indigo, violet.

Noam Hassenfeld (4:32)

So why isn't color as simple as just longer wavelength, red, shorter wavelength, blue? Why is color mysterious?

Bevil Conway (4:43)

If color were just wavelength, then an object under blue light would look blue, and the same object under yellow light would look yellow.

That wouldn't be very helpful because what you want is a signal that tells you about objects immune to the lighting condition. You want them to always have that color. A perfect example is like take a peach. If you look at a peach outside and you look at it inside, it's always going to look like peach color. But if you looked at the pattern of wavelengths that are coming off of the peach, they're very different inside and outside under different lighting conditions. They should be different colors if color were just wavelength, but they're not different colors. Those two different compositions of wavelengths look the same color.